Page 246 - Electrician - TT (Volume 1)

ELECTRICIAN - CITS

11 Temperature gauge

12 Tap changer manually operated
13 Cooling tubes.
14 Tank
15 Wheel

16 Oil out drain box
17 Earth

Pressure Release Device
• Uncontrolled increases in pressure may create the danger of explosion with all the possible harm and damages.
• Control pressures inside tanks.
• Designed to discharge the pressure increases in a very short time period (a few thousandths of a second).

• They are widely used in the metal tanks of oil-cooled electric transformers.
• One or more pressure relief device with discharge sizes proportional to the volume of oil contained in the
transformer
• Sudden and violent short circuits inside tanks, instantly generate an enormous amount of gas with a great
increase in interior pressures.
Buch Holz Relay
It is a sort of automatic circuit breaker which trips off the transformer in the case of transformer fault, due to
insulation failure or short circuit. It consists of twomercury float switchesonefor alarm contact, it enables when
excess gas pressure building inside main tank and the other for trip circuit which operates when the temperature
of oil increased further.
Breather
• Silica gel is used in breather

• capacity of absorbing moisture.
• When air passes through these crystals in the breather; the moisture of the air is absorbed by them.

233

CITS : Power - Electrician & Wireman - Lesson 41-49 CITS : Power - Electrician & Wireman - Lesson 41-49